1. Field of the Invention
This invention relates to an improved interconnection for integrated circuit structures and a method of making same. More particularly, this invention relates to a novel multilayer interconnection for integrated circuit structures having more than one conductive metal layer.
2. Description of the Prior Art
Conventionally, aluminum base metal, i.e., aluminum or an alloy of aluminum, is used to form the interconnections or "wiring" between components and devices in integrated circuit structures. Such uses of aluminum include the interconnections or vias used between different layers or levels of metal such as aluminum as well as for the contacts to individual elements of an active device in the integrated circuit structure such as the collector, base, and emitter contacts of a bipolar transistor or the source, drain, and gate electrodes of an MOS device.
Aluminum is not the only metal which is or can be used for such purposes. Both platinum and gold metals have also been used in such applications. However, aluminum remains by far the most prevalently used metal in integrated circuit structures because of its superior combination of low cost, low weight, and good conductivity.
However, the use of aluminum in integrated circuit structures for interconnections, contacts, and the like is not without its problems. When aluminum is used as an electrical contact to an electrode region of an active device formed in silicon, the aluminum and silicon may interdiffuse which can cause the aluminum to migrate down into the silicon substrate below the junction formed between the doped region and the substrate, e.g., below the source or drain regions, thereby shorting out the device.
Furthermore, when a layer of aluminum is used as the horizontal interconnection between devices or elements of a device, some areas of the aluminum interconnect may form hillocks or spikes upon subsequent exposure to processing temperatures above 400.degree. C. which can, in turn, result in formation of an electrical short from the aluminum layer through an overlying insulating layer to another metal layer thereon.
The use of a conductive material such as a titanium-tungsten alloy over an aluminum layer or between two aluminum layers is known. Lin et al, in an article entitled "Linewidth Control Using Anti-Reflective Coating for Optical Purposes", IEDM International Electron Device Meeting, San Francisco, Calif., Dec. 13-15, 1982, at pp 399-402, discuss the use of various antireflective coatings such as titanium-tungsten, vanadium, and polysilicon on aluminum to lower the reflectivity of aluminum for photolithographic purposes.
Harrison et al in an article entitled "The Use of Anti-Reflective Coatings for Photoresist Linewidth Control", Kodak Microelectronics Seminar, San Diego, Calif., November, 1983 also discuss the use of anti-reflective coatings such as vanadium, titanium-tungsten, molybdenum, titanium, and polysilicon on aluminum-silicon materials. This latter reference also discloses the previous use of titanium-tungsten under Al-Si as a barrier layer to prevent aluminum spiking in the silicon substrate.
The use of a layer of titanium-tungsten between two aluminum layers in an integrated circuit structure as an etch stop is discussed in Pierce et al U.S. Pat. No. 4,267,012.
While the use of other materials such as titanium-tungsten between adjoining layers of aluminum is, therefore, known, it has been found that problems such as the diffusion of aluminum into an underlying silicon substrate may actually be exacerbated by the presence of materials such as an alloy of titanium-tungsten over the aluminum. Apparently this is due to the fact that a titanium-tungsten alloy and aluminum can interact to form an intermetallic compound (Ti.sub.x Al.sub.y W.sub.z) which actually has a higher solubility for silicon than the solubility of aluminum for silicon.
It would, therefore, be desirable to provide an interconnection in integrated circuit structures having more than one conductive metal layer which would eliminate or at least mitigate some or all of the problems caused by the use of aluminum metal as the interconnection.